Polishing machines for grinding and polishing the ends of fiber optic cables are usually of the type having a rotating abrasive disk that is maintained relatively flat. The optical fiber is secured in a fixture having a flat bottom. The end of the optical fiber that is to be polished projects slightly below this bottom surface, sometimes under the urging of a spring mechanism to control the forces on the fragile optical fiber. The fixture, with its fiber optic cable attached, is carefully lowered onto the rotating abrasive disk and made to undergo a standard polishing pattern such as circular or figure eight. The polishing usually occurs in a particular segment of the rotating disk so that, as polishing continues, the same abrasive surface is continually presented to the tips being polished. There are usually three or more stages of polishing that must be done in sequence, from relatively course abrasive to very fine. Prior to machine polishing, however, it is usually necessary to hand polish the tips to remove the protruding fiber stubs to prevent damage. In certain prior art polishing machines, during the final stage the bottom surface of the fixture contacts the abrasive disk so that the end of the optical fiber is polished to a flat surface flush with the bottom surface of the fixture. Other prior art polishing machines rely upon the tips of the optical fibers themselves in contact with the abrasive surface to maintain the axes of the fixture and the cables somewhat perpendicular to the surface of the abrasive material. In these machines the fixture itself does not contact the abrasive material, therefore, the quality of the final polished surfaces of the cable is dependant upon the amount of ferrule projection below the bottom of the fixture. Such projections will vary due to variations in the manufacturing of the terminated cables. That is, when the cables are loaded into the fixture they are positioned with respect to some feature of the connector such as a shoulder. This results in the tips of the optical fibers extending below the bottom surface of the fixture by varying amounts, the three tips that extend the farthest being the ones that establish the initial angle between the axes and the abrasive surface. With such an arrangement some of the optical fibers are polished more than others resulting in inconsistency and varying quality.
What is needed is a polishing machine and method of operation that controls the relative motion of the tips of the optical fibers with respect to the abrasive material so that fresh abrasive is always presented to the tips for efficient and high quality polishing. To eliminate the need for preparatory hand polishing, the machine should allow for relatively slow engagement during the initial stage of polishing with a more normal rapid engagement during later stages. Additionally, the tips of the optical fibers should be located in a plane that is parallel with the abrasive surface prior to polishing and the fixture that holds the fiber optic cables should be maintained in this plane during polishing, thereby obviating the alignment and quality problems mentioned above or the need for the fixture to contact the abrasive material to maintain vertical alignment.